Method and apparatus for heat transfer



March 24, 1964 w. F. JAEP 3,125,861

METHOD AND APPARATUS FOR HEAT TRANSFER Filed Aug. 5, 1965 4 Sheets-Sheet l INVENTOR WILLIAM F. JAEP ATTORNEY March 24, 1964 w. F. JAEP 3,125,861

METHOD AND APPARATUS FOR HEAT TRANSFER Filed Aug. 5, 1963 4 Sheets-Sheet 2 FIGJZII 59C MAGNETIZATION 2 4 l'o l2 msTANcE Mone Ron (om.)

TEMPERATURE vERsus DISTANCE ALONG GRADIENT Roo AT WHICH TRANsmoN ls 50% COMPLETE e0 F' A INVENTOR w|LL|AM F. JAEP 500 8 ATTORNEY 2 4 6 DISTANCE ALONG ROD (Cm.)

BY @MM March Z4, 1964 w. F. JAEP METHOD AND APPARATUS FOR HEAT TRANSFER 4 Sheets-Sheet 3 Filed Aug. 5, 1963 INV ENTOR WILLIAM F. JAEP March 24, 1964 w. F. JAI-:P 3,125,861

METHOD AND APPARATUS FOR HEAT TRANSFER Filed Aug. 5, 1965 n 4 Sheets-Sheet 4 wv/mf sff M/l/f l/l/r ELEcrRouAcNET swncH 0^ cAu FoLLowER VACUUM PUMP INVENTOR WILLIAM F. JAEP ATTORNEY United States Patent 01 3,125,861 METHD AND APPARATUS FOR HEA'I` TRANSFER William Frederick Jaep, Wilmington, Del., assigner to E. I. du Pont de Nemours and Company, Wilmington, Del., a 'corporation of Delaware Filed Aug. 5, 1963, Ser. No. 391,934 2l Claims. (Cl. S2-3) This invention relates to a method and apparatus for obtaining heat transfer, and particularly to a heat transfer method and apparatus which generally may be termed thermomagnetic in nature and which utilizes la substance which undergoes a first-order phase transition with accompanying change in internal energy content under the influence of a magnetic field.

The apparatus of this invention is a form of heat pump, the best-known conventional example of which is probably the domestic refrigerator, which depends for operation on the cycling of a fluid between liquid and vapor states. In a common type of such a refrigerator, the working fluid cycles between a high pressure and a low pressure region, the pressure differential between which is about atmospheres. To maintain this pressure differential, a mechanical system including a compressor or pump operated by an electric motor is required, with attendant problems of lubrication, vibration, noise and inconvenience resulting from operation of the several mechanisms.

A completely different type of heat pump, employed only at very low temperatures, utilizes a paramagnetic material as the working substance. When such a substance is exposed to a strong magnetic field at a very low temperature near absolute zero and the magnetic field is then reduced to zero, the temperature of the substance drops slightly due to the so-called magnetocaloric effect. This technique is described, for example, by Gorter, Progress in Low Temperature Physics, Interscience Publishers, New York (1955), vol. 1, pp. S-321. This same principle is utilized at high temperature levels near the Curie point by devices of the design taught in U.S. Patent 2,589,775. The magnitude of the heat transferred per cycle utilizing the magnetocaloric effect is, however, relatively small, because there is no accompanying latent heat. Consequently, this type of refrigeration has found only very special applications, such as at extremely low temperatures where other refrigeration means have proved ineffective.

This application is a continuation-in-part of my prior applications Serial No. 167,555, filed January 22, 1962, and Serial No. 19,373, filed April l, 1960, now forfeited.

An object of this invention is to provide a new method and apparatus for effecting heat transfer having a higher thermal efficiency and a greater magnitude of heat transfer per cycle than magnetocaloric devices. Another object of this invention is to provide a method of heat transfer and a heat pump arrangement which is ideally suited to operation throughout an exceedingly wide range of temperatures and which, conversely, can be readily designed for optimum service at specific temperature extremes. Another object of this invention is to provide a basic thermomagnetic heat pump system which is simple in design and which dispenses with many of the mechanical appurtenances essential in conventional heat pump sys-tems. Yet another object of this invention is the provision of such a heat transfer arrangement which is capable of easy adjustment and calibration for varying its operation to accommodate varying conditions as desired. A further object is the provision of a thermomagnetic element or component which has broad utility in many types of energy transfer devices in addition to heat exchange apparatus.

3,125,861 Patented Mar. 24, 1964 ice 2 The manner in which these and other objects of this invention' are attained will become apparent from the following detailed description and the drawings, in which: FIGURE I is'a partially schematic representation in vertical 'cross-section of a`sing1e stage heat pump according to this invention wherein the details of electrical power supply and control circuitry are omitted for simplification of the showing,

FIGURE II is a vertical cross-sectional of a four-stage apparatus incorporating four separate heat pumps of the design shown in FIGURE I disposed in cascade arrangement,

` FIGURE III is a partially schematic side-elevational view of an embodiment of a single-stage heat pump according to this invention inclusive of the associated electrical circuit utilizing a stationary vehicle and a moving heat source and sink,

FIGURE IV is a sectional enlarged view in side-elevation of the vehicle enclosure of the apparatus of FIG- URE III,

FIGURE V is a section taken on line V-V of FIG- URE III,

FIGURE VI is a schematic view of an arrangement for electroplating a longitudinally tapered layer of chromium on a rod formed of the heat transfer substance of this invention in order to produce a graded variation in composition and properties along the rod length,

FIGURE VII is a graphical representation of the variation in magnetization along the length of a rod having varied composition along its length.

FIGURE VIII is a graphical representation of temperature versus the location along a varied composition rod at which the solid-phase-to-solid-phase transition is 50% complete,

FIGURE IX is a longitudinal cross-sectional view of a heat exchange portion of a refrigerator arrangement embodying features of the present invention taken on line IX-IX of FIGURE X,

FIGURE X is an end view of the refrigerator arrangement of FIGURE IX, and

FIGUREv XI is a schematic diagrammatic showing of the over-all refrigerator arrangement, or system, portions of which are shown in FIGURES IX and X.

FIGURE XII are illustrative examples of the patterns in which the portions of the thermomagnetic body may be arranged.

Generally, the method and apparatus of this invention utilizes a thermomagnetic control or actuating means comprising, as a heat transfer medium, a substance which vdisplays a first-order solid-phase-to-solid-phase transition with accompanying relatively large change in internal energy content in going through the transition, magnetic means for cyclically inducing said transition in a direction such as to lower the temperature of the substance when one solid state phase is attained and to increase the temperature when Ythe other solid state phase is attained, and a heat source and sink relative to one of the solid state phases individually adapted to effect heat transfer sequentially with respect to said substance. If desired, a means may be provided to vary the operation of the apparatus as desired to compensate for varying operating conditions. The substances employed as the heat transfer medium according to this invention, hereinafter for convenience referred to as the vehicle, are metallic in nature and possessed of the capability of being traversed, at least in part, through a first-order solid-phase-to-solid-phase transition'under the infiuence of a magnetic field of appropriate strength. The magnetic field can, if sufficiently strong, effect ythe full transition; however, somewhat weaker fields can induce the transition to run the full course if the field is sufficient to merely initiate the transition, lwhich is thereafter carried to completion by heat transfer between the substance and its surroundings. As a result heat transfer can, as a practical matter, be conducted isothermally with respect to the substance per se of the Vehicle by supplying or removing heat, balancing the latent heat associated with the transition while the transition is occurring, preferably, or promptly thereafter, so that losses to the outside are minimized. In either case, the magnetic field inducing the transition lowers the temperature of the vehicle substance at the outset, thereby setting up the temperature differential which is necessary to effect heat transfer.

Coincidentaily with traversal of the transition there occurs a change in the magnetic state, which constitutes going from paramagnetic or anti-ferromagnetic on the one hand to ferromagnetic or ferrimagnetic on the other, although the specific magnetic states are, in some cases, diiiicult to identify and it appears that different magnetic states can, upon occasion, exist side-by-side in localized regions of a given specimen. Moreover, in substances in which the transition occurs over a relatively broad range of magnetic field strengths the change from one magnetic state to another can be quite gradual, and the progress perceptible to the investigator therefore somewhat ambiguous and ill-defined. The reasons for these effects may lie in the non-homogeneous composition of a given specimen, or in the persistance of metastable states, and there are probably other causes not resolved at this time. Nevertheless, the substances are all impelled through their transitions by a magnetic field, although somewhat larger fields are required than in the case of ideal specimens. This is not disadvantageous from the standpoint of this invention, because the magnetic states are completely incidental to operation except in the special situation where magnetic attraction is utilized to effect physical transport of the vehicle from heat transfer relationship with respect to a source to heat transfer relationship with respect to a sink. Then, of course, it is essential that there be a relatively sharp diffedence in magnetic properties on one side of the transition as opposed to the other, all as hereinafter brought out with respect to the embodiment of FIGURES I and II.

This first-order transition is such that it can be induced to occur at preselected temperatures, within limits, by the application of compressive force to the substance, as a result of which there occurs an alteration in the temperature response which is, for the antimonides hereinafter described, of a magnitude of about 2 C. per 15,000 lbs/sq. in. of compression in the direction of increasing temperature for the mid-point of the indication span. This not only affords a means for small scale changes in characteristics as an aid `in `calibration by the use of pressure-loading set screws or other means, but also makes possible a response based on combined temperature-pressure interaction provided, of course, that the contribution allocable to each agency is identifiable.

The transition temperature zone of the substance may also be controlled to some extent by varying the intensity of the magnetic iield applied.

A iirst-order transition is always accompanied by a change in internal energy in the substance undergoing the transition, and this change is manifested by a latent heat which, in the vehicle state in which the internal energy con-tent -is lowered, becomes available as a sensible heat for transfer by conduction and the other modes of heat transfer to an adjacent heat sink with respect to which a positive thermal gradient exists. Conversely, where the vehicie state past the transition point is such that the internal energy content is elevated, the vehicle seeks to absorb heat from its environment and will, accordingly, remove heat from a source with respect to which a negative thermal gradient exists. Thus, a heat pumping action is obtained which, upon suitable choice of design conditions, can be made to function conjointly as a heating and refrigerating means.

The substances employed in the vehicles and gradient objects of this invention are possessed of the characteristic of abruptly changing in a controllable manner their saturation induction with changing temperature from a nonmagnetic to a magnetic state in the course of the firstorder transition from one solid state phase to a second solid state phase. This change in phase occurs preferably with no change in crystal symmetry. It is preferred that this change be from an anti-ferromagnetic state on the one hand to a ferromagnetic or ferrimagnetic state on the other. This characteristic is in addition to normal Curie point or Neel point behavior of these substances.

The temperature at which the transition occurs is affected by changes in composition of the magnetic phase and can be adjusted to suit a particular device. The most useful compositions exhibit a saturation induction below the transition temperature, which is not more than about 1/10 0f the maximum saturation induction above this temperature.

A first-order transition, also known as a transition of the first kind, is one in which a discontinuity occurs in the first derivatives of the Gfifbbs `free energy. For example, there are discontinuities in the first derivative with respect to temperature, i.e., entropy, with respect to pressure, i.e., in volume, and for .a magnetic material with res ect to magnetic field, ie., in magnetization.

A second-order transition is one in which the second derivative of the free energy function is discontinuous but the first derivative is continuous. In other words, at a second-order transition energy, volume, and in a magnetic substance magnetization changes continuously but the temperature derivatives of these quantities have singularities. The Curie point in a magnetic material is an example of a second-order transition.

Further `discussion of first and second-order transitions is found in Swalin, Thermodynamics of Solids, John Wiley & Sons, Inc., New York, 1962, pp. 72-73, and in Phase Transformations in Solids (Symposium at Cornell University, August 23-28, 1948), John Wiley & Sons, Inc., New York, 1951, Chap. I, by L. Tisza, pp. 1 and 2. Quotations from these references are given below:

If a transition occurs with a discontinuity in first derivatives of the free energy, it is called a first order transition.

If a transformation is discontinuous in its second derivatives of the free energy function, it would be identified as second order.

The transformation from the ferromagnetic to the paramagnetic state is considered as an example of a second order transition.

Tiszait is well known that there are two kinds of phase transitions: the first kind, called also of first order, in which energy, volume, and crystal structure change discontinuously; the second kind, frequently called Curie points in which energy and volume change continuously, but the temperature derivatives of these quantities have singularities.

As defined in the International Dictionary of Physics and Electronics, Van Nostrand, second edition, copyrighted in 1961, the Nel temperature is the transition temperature for an antiferromagnetic material, at which maximal values of magnetic susceptibility, specific heat, and thermal expansion coe'icient occur.

Among compositions useful as in the devices of this invention are compositions as more fuliy described in copending U.S. patent application Serial No. 181,744, filed March 22, 1962, by T. I. Swoboda, which contain at least two transition elements selected from groups V-B, VI-B, and VII-B of the periodic table, of which at least one is taken from the first row of said transition elements, and at least one element of group V-A selected from As and Sb, and which are further characterized by having a maxi-l mum saturation induction at a ,temperature above K. but below the Curie point of the composition.

` `The periodic table referred to herein is the one appearing in Demings General Chemistry, lohn Wiley & Sons, Inc., th edition, Chap. 1l.

In these compositions, said group V-A element(s) constitutes 5-40 [atom percent of the whole and will generally be in the range of 5-35 atom percent. It will be understood that at least one group V-A element of the group consisting of arsenic and antimony, is always present in the compositions. Nitrogen, phosphorus and bismuth may also be present. Of the remaining components, theV transition metals of groups V-B, VI-B and VII-B of `the periodic table, i.e., at least two of V, Cr, Mn, Nb, Mo, Ta, W and Re, of which at least one is selected from Y, Cr and'Mn, constitute from 35-95 atom percent, any other element present being a metal from groups Il-lV of the periodic table in an amount of not more than 30 atom percent.` Suitable examples of such other elements are cadmium, gallium, indium, lead, thallium, tin, zirconium, scandium, yttrium, magnesium and zinc. Ordinarily one ofthe transition metals enumerated above will constitute the major proportion of the transition metal content of the composition while the second transition `metal will be .present in minor proportion. However, in no case will the content of the second transition metal be less than 0.1 atom percent based on the total composition.

Compositions which are particularly useful contain antimony, manganese, and at least one additional transitionY metal, particularly chromium, vanadium, molybdenum or niobium, and optionally one or more additional elements selected from the group consisting of indium, cadmium, lead, zirconium, tin, gallium, thallium, scandium, yttrium, magnesium and zinc.

Examples of useful compositions are those containing antimony, 5-40 atom percent; manganese, 35-9l.9 atom percent; at least one element of the group chromium and vanadium, 0.1-38.5 atom percent; and optionally an element of the group Cadmium, gallium, indium, lead, thallium, tin, zirconium, scandium, yttrium, magnesium and zinc, 0-30 atom percent, the percentage values being so chosen as to total 100%.

Other useful compositions contain antimony, 5-35 atom percent; manganese, 25-75 atom percent; at least one element of the group molybdenum and niobium, 0.1-50 atom percent; and optionally an element of the group cadmium, gallium, indium, lead, thallium, tin, zirconium, scandium, yttrium, magnesium and zinc, 0 30 atom percent.

The foregoing compositions can lbe described by the formula MnaXbZcSbd, where X is chromium, vanadium,

vmolybdenum, or niobium; Z isindium, cadmium, gallium,

lead, thallium, tin, zirconium, scandium, yttrium, magnesium or zinc; and a, b, c, and d are the atomic proportions of the elements employed and are chosen so as to provide percentage compositions in the ranges stated above. Compositions, in which X and/ or Z represent a combination of two or more elements, can also be employed in the devices of this invention.

Particularly useful compositions are those containing S35-.91.9 atom percent manganese, 8-35 atom percent antimony, and 0.1-38.5 atom percent of an additional element of the group chromium, vanadium and mixtures thereof. These compositions can be described by the formula MnaXbSbd, where X is chromium and/or vanadium, and a, b, and d are the above indicated atomic proportions of the elements, a, b, and d totalling 1. Especially useful compositions have the formula Mn2 XXXSb, where x is 000E-0.41, it being understood that the sum of the subscripts to Mn, X and Sb is 3.

Other useful compositions are those containing antimony, 5-35 atom percent; manganese, 35-70 atom percent; at least one element of the group chromium and ,vanadium,`0 .825 atom percent; and an element of the group cadmium, gallium, indium, lead, thallium, tin,

zirconium, scandium, yttrium, magnesium and z inc, O-30 atom percent, the percentage values being so chosen as to total The foregoing compositions are examples of materials which undergo a iirst-order solid-phase-to-solid-phase transition upon the application of a magnetic field, traversal of the transition being, in this case, accompanied by a fall in temperature ofthe substances and a change from the non-magnetic to the magnetic state. However, yet other substances which meet the general requirements hereinbefore set forth for a vehicle are also useful. Thus, for example materials which exhibit a first-order transition in Vthe reverse sense, i.e., in going from a magnetic to a non-magnetic state with accompanying rise in temperture can also be employed. Representative of the latter type of material is manganese arsenide and, obviously, other substances having the delineated characteristics are eflicacious for the purposes.

As specific illustrations of thevcompositions described above may be mentioned manganese-chromium or manganese-vanadium antimonides which contain manganese in an amount of S35-91.9 atom percent, chromium and/or vanadium in an amount of OLI-38.5 atom percent, and 8-35 atom percent of antimony. Certain of these compositions can be represented by the formula Men-z XMxSb, where M is Cr or V, and x is 0.003-0.4l. Manganese-chromium antimonide according to this formula exhibits a transition at room temperature, about 300 K. when x is about 0.1.

Other particularly desirable compositions for use in the present invention are manganese-antirnony arsenide and manganese-germanium antimonide containing 61-75 atom percent manganese, up to 20 atom percent arsenic or germanium, and the balance antimony. Further desirable compositions are manganese-cobalt antimonide, and manganese-zinc antimonide. As indicated above, the presence of additional elements in the composition may sometimes have a beneficial effect. It will be appreciated that the foregoing vspecific compositions are illustrative only and that still other compositions meeting the requirements for a first-order solid-phase-to-solid-phase transition can be employed.

Iron-rhodium alloys and iron-rhodium alloys containing up to 20 atom percent of at least one other element are also useful as working elements `in this invention. Suitable alloys include those described by Fallot, Revue Scientifique, 77, 498 (1939); Kouvel et al., General Electric Research Report No. 61-RL-2870M; copending U.S. applications Serial Nos. 177,229 and 177,230, filed March 5, 1962, by P. H. L. Walter; application Serial No. 192,- 06,0, filed May 3, 1962, by P. H. L. Walter; and application Serial No. 192,059, led May 3, 1962, by T. A. Bither. These magnetic compositions consist essentially of iron and rhodium in major proportion and at least one other metal rin minor amount ranging from 0.010.20 atom proportions. These new magnetic compositions are alloys of the formula `FeRh[xl\/i]c, wherein M represents: (l) at least one A-group element selected from the group beryllium, magnesium, aluminum, gallium, indium, silicon, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, and tellurium, i.e., a member of group II-A of the periodic table of the elements of atomic number 4-12 or a member of groups III-A, IV-A, V-A, VI-A of the periodic table of the elements of atomic number 13 through 83, inclusive, and x is an Iinteger from 1 to 6 and generally 1 to 2; (2) at least one transition metal of atomic number 39-48 and 57780, inclusive, other than rhodium, i.e., yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury, and x is an integer from l to 6 and generally from 1 to 2; (3) at least one transition metal of atomic number 21-30, inclusive, other than iron, viz., s candium, titanium, vanadium, chromium, manganese,

'i' cobalt, nickel, copper, and zinc, and x is an integer from 1 to 6 and generally 1 to 2; or (4) at least one rare earth metal of the lanthanum or lanthanide series of the periodic table of the elements of atomic numbers 58-71, inclusive, viz., cerium, praseodynium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbiurn, thulium, ytterbium, and lutetium, and x is an integer from 1 to 14, and generally 1 to 3. In all these iron-rhodium compositions, a and b, which can be alike or different, are numbers ranging from 0.8-1.2, and c is a number ranging from G01-0.20, and in the instance when xZ, the requisite cs can be alike or different but still must fall in the indicated range. These subscript numbers refer to the atomic proportions of the elements in the final alloy. M can be different within the same deiined group when x is greater than 1.

Further compositions which can be employed in the vehicles and gradient objects of this invention have a tetragonal crystal structure and contain manganese in an amount of at least 40 atom percent, a second metallic component selected from iron, cobalt, nickel, copper, and zinc, in an amount of 0.6-25 atom percent, and at least one of arsenic, antimony and bismuth in an amount of 25-40 atom percent. Additional components selected from the elements of groups III-A, III-B, IV-A, and IV-B, nitrogen and phosphorus in an amount of -25 atom percent may also be present. These compositions are described more fully in copending U.S. patent application Serial No. 66,194, filed October 31, 1960, in the name of T. l. Swoboda. Additional useful compositions are MnSGez and CrS.

Still other compositions useful in the present invention are described in application Serial No. 66,195, liled October 31, 1960, in the name of T. A. Bither. These compositions have a tetragonal crystal structure and contain a single transition metal selected from vanadium, chromium, manganese, iron, cobalt, or nickel in an amount of 61-75 atom percent, and from 25-39 atom percent of at least two elements selected from gallium, germanium, selenium, tellurium, arsenic, antimony and bismuth, of which at least the major atom percent consists of arsenic, antimony, and/or bismuth.

Other useful compositions are represented by the formula Mn2 y XTySbZIna, where T is chromium and/ or vanadium, T is one or more of iron, cobalt, nickel and copper, x is 0.003-0.25, y is 0.003-0.25, z is U50-1.00 and a is 0-0.50. These compositions are more fully described in application Serial No. 261,784 of W. W. Gilbert and T. I. Swoboda, filed February 28, 1963.

Processes for preparing compositions useful in the elements of this invention are described in the foregoing applications and in application Serial No. 120,679 of W. W. Gilbert, tiled June 29, 1961.

As an example of a ternary composition which demonstrated a first-order transition with concomitant change in sensible temperature, a single crystal weighing 8 g. was prepared having the composition: 45.62% Mn, 2.25% Cr, 0.12% In and 52.01% Sb. When this crystal was thrust suddenly between the poles of a permanent magnet having a rated field strength of 5000 oersteds, the temperature of the crystal, measured by a thermocouple attached thereto, decreased 0.67 C., indicating that the internal energy level of the substance making up the crystal had increased, thereby establishing a heat demand on the part of the crystal with respect to the environment.

In a second test using a manganese-chromium antimonide containing 45.54% Mn, 2.81% Cr and 51.67% Sb, sudden exposure to the same magnetic iield produced a temperature decrease of 1 C.

A simple design of heat pump adapted to parallel the foregoing experimental results, but on a somewhat larger scale, is that shown in FIGURE I. Here the vehicle, or thermomagnetic operating or control means, consists of a reciprocable element or slug 1 of a substance or material displaying a first-order transition as hereinbefore described under the influence of a magnetic field. In this instance it is convenient to employ a slug of cylindrical shape, although this is not essential. The material chosen was strongly magnetic when in a magnetic iield and substantially non-magnetic in the absence of a field, so that this phenomenon could be utilized to move the slug from the lowermost heat reservoir 5 into contact with the upper heat reservoir 4 located vertically above 5 under the influence of the magnetic iield imposed by copper coil 3 which was disposed nearer to reservoir 4 than to reservoir 5. As shown, heat reservoirs 4 and 5 are merely solid metal plates fabricated from a non-magnetic substance such as copper, as an example. Since slug 1 was magnetic in one of its two states, a physical barrier was provided between slug 1 and coil 3 in the form of polytetrauoroethylene resin tube 2 disposed between the reservoirs.

In operation, with all components at the same initial temperature, when an electric current is passed through coil 3 in sufficient amount, a magnetic ield is impressed on slug 1, which traverses the substance through its firstorder transition, thereby lowering the sensible temperature of the slug. The slug, being now converted to its magnetic state, rises within 2 under the influence of the unbalanced field of coil 3 until it abuts against the lower face of heat reservoir 4, there remaining in close contact therewith and withdrawing heat from 4 as the source, to adhere to conventional thermodynamic terminology, by thermal conduction. After an appropriate interval of time during which the temperature of source 4 falls toward the temperature of slug 1, the ow of current through coil 3 is switched off. The material of slug 1 immediately traverses the transition into its other (nonmagnetic) state, whereupon the internal energy requirements are decreased, thereby raising the sensible temperature above that of the initial equilibrium level. Simultaneously, slug l drops under the influence of gravity to its original position in abutment with the upper face of 5, which in this case is the sink, thereby transferring heat to it by thermal conduction. After the passage of a suitable interval of time to permit heat transfer out of the vehicle, the entire cycle is repeated.

A test apparatus constructed according to FIGURE I utilized a cylindrical slug 1 measuring 7 mm. in diameter and 9 mm. long made up of the quaternary composition, all percentages being by weight: Mn 45.62%, Cr 2.25%, In 0.12%, and Sb 52.01%. Slug I was placed within a vertically disposed polyethylene tube 2 having an internal diameter of 10 mm. and a length of 15 mrn. The ends of the tube were covered at top and bottom by copper plates, these corresponding to source 4 and sink S, respectively. The device was placed within a horizontal magnetic field of approximately 7000 oersteds strength provided by an electromagnet. The apparatus was operated upon a lO-minute cycle, current being permitted to pass through coil 3 for 5 minutes, following which current flow was discontinued for 5 minutes. Even under these relatively unfavorable conditions of operation, the temperature of plate 4 was progressively reduced until, after 50 minutes, plate 4 measured 1.5" colder than plate 5.

In the absence of the cooling effect due to cycling of the vehicle through its iirst-order transition, heat liberated by the magnet as a result of resistance losses and the like was suiiicient to maintain upper plate 4 at a temperature 1 C. higher than that of lower plate 5 as a result of the asymmetric location of coil 3. It will be understood that, if desired, slug l can be impelled from sink 5 to source 4 cyclically by providing a mechanically driven rigid rod attached thereto and running the rod through a suitable slide bearing in one or both of the plates in analogous manner to a piston-piston rod construction, thus eliminating the magnetic reciprocation. It is thereby possible to eliminate tube 2 as well; however, the guide tube can also be dispensed with while retaining magnetic lifting by simply slidably mounting slug 1 on a rigid wire or rod disposed centrally of source 4 and sink 5 by providing the slug with a longitudinal drilled passageway threaded through by the rod.

It has been found possible to shift the transition points of substances employed as vehicles according to this invention by judicious variation of the chemical compositions, so that the first-order transition hereinbefore described can be made to occur at progressively staged temperatures from one vehicle to another upon the application of the same, or approximately the same, magnetic fields. This affords a method of multi-staging the heat transfer, with resulting relatively great expansion of range, by cascading a number of individual heat pumps, and FIGURE II shows such an arrangement provided with four stages made up of pumps of identical design with FIGURE I. As mentioned in the preceding description, it has been found that the transition points of substances involved as the vehicle can be shifted within limits by varying the intensity ofthe magnetic field applied and, in addition, these transition points can be shifted within limits by varying the pressure on the substance of which the vehicle is comprised.

In FIGURE II it is assumed that the low-temperature source is the topmost plate 8 of the series, whereas the high-temperature sink is the bottommost, i.e., 9. The several stages are indicated at A, B, C, and D, the bodies of thermomagnetic material, or vehicles of which have progressively increasing transition temperatures in the order named from `top to bottom of the apparatus by appropriate preselection of the several magnetic vfield intensities applied or of the several compositions. It has proved practicable to obtain a substantially continuous spectrum in transition temperature levels in 3-5 C. intervals from stage to stage by careful adjustment of the analysis of the individual quaternary compositions hereinbefore described, so that imposition of substantially the same magnetic iield via the associated coils is elfective in transferring heat from each next-higher unit to its next-lower neighbor in sequence. Under these circumstances the coils can all be connected in series electrical circuit if desired or, for somewhat greater flexibility in proportioning fields to transition temperatures, each can be separate. Also, the slugs, or thermomagnetic operating means, of individual stages can optionally be impelled magnetically upwards in unison, or in any other time sequence which may be convenient, since the several plates function as temporary heat reservoirs of enough capacity so that this is nota critical consideration.

The embodiment of apparatus shown in FIGURE I utilizes stationary heat reservoirs and a movable vehicle; however, heat pumping according to this invention can be accomplished equally well by, in effect, moving a fluid component of the reservoir relative to the vehicle, and FIGURE III depicts such an arrangement in single-stage.

Here the iluid components are `two bodies of liquid medium, each of which has its own exclusive circulatory circuit, which liquids are pumped in sequence through a stationary mass of vehicle 12 in co-ordinated time phase with the application of the magnetic field effecting vehicle transition, sothat rst one liquid is cooled, i.e., is a source, and then the other Vliquid heated, i.e., isa sink, in alternation.

As shown in FIGURE IV, the thermomagnetic component or vehicle `12 preferably comprises a body or mass of granular substance, which may be of the order of mesh size, which is retained within an enclosure 14 fabricated from at sheets ,on atleast the top Vand b ottom sides to permit dispositionclosely adjacent to lthe opposed pole faces of .the electromagnet 15, as shown in `FIGURES III and V. Screens 16 and 17 at opposite ends of 14 retain vehicle 12 in place while permitting relatively free passage of uids therethrough, and one port 18 is connected to three-way valve 19 whereas the other port 20 is connected to three-way valve 21.

The cold reservoir (heat source) 24, i.e., the reservoir storing cold liquid, receives liquid drawn in a clockwise direction from enclosure 14 through valve 19 by pump 27 and delivered through line 28 discharging into 24. During the same time interval, cold reservoir 24 is in open communication with enclosure 14 through valve 21 and port 20, thus effecting recirculation of cold liquid to 14. Similarly, warm reservoir (heat sink) 29, i.e., the reservoir storing the warm liquid, receives liquid drawnfroin enclosure 14 in a counterclockwise direction through valve 21 by pump 30 with output connected to line 31, and this liquid is recirculated to 14 through the upper llow passage of valve 19 and port 18 when these vare connected together during the following half cycle.

The electrical circuit for the embodiment of FIGURE III is quite simple and includes coils 33 and 34 wound in series around the opposed poles of 15, which coils are connected in circuit with a D.C. power source, representedv generally at 35, through a single-pole, singlethrow switch 36. Switch 36 is alternately closed and opened, respectively, for preselected intervals of time by a conventional timing controller 37 synchronously with rotation of three-way valves 19 and 21 from their positions shown in FIGURE III to their opposite positions,

as indicated schematically by the broken lines drawn thereto.

In operation, with three-.way valves 19 and 21 set as shown in FIGURE III, if a suciently strong magnetic eld is applied to the vehicle by switching in electrical current through windings 33 and 34, the vehicle is induced to pass through the transition, during which time its temperature drops, abstracting heat from the liquid circulated through the cold circuit by pump 27. After allowing a sufcient time interval to establish near-thermal equilibrium between the cold liquid and vehicle 12, if the current is now switched off vehicle 12 passes through the transition reversely, thereby raising its temperature and, with valves 19 and 21 set to their positions opposite from those represented in FIGURE III, pump 30 draws hot liquid from reservoir 29 through vehicle 12, valve 21 and return line 31, thereby abstracting heat from the vehicle. After an appropriate interval, cold reservoir 24 is placed on stream again and the entire cycle repeated, thus removing heat from the cold fluid and adding heat to the warm uid during successive increments of time.

The embodiment of FIGURES Ill- V is intermittent in operation as regards the cold heat source on the one hand and the warm heat sink on the other; however, if two separate vehicles are employed in parallel relationship with alternately switching liquid flow control valves there is obtained continuous operation, with one vehicle abstracting heat simultaneously with the other vehicles delivery of heat.

Closed ow circuit handling of liquid as described for the embodiment of FIGURES III-V is particularly suitable for single-stage heat transfer, although cascading can be resorted to in the same manner as shown in FIG- URE II if multiple staging is desired. However, for the latter a somewhat simpler system involves using a single reversing pump and delivering the liquid back and forth through the stationary vehicle in its enclosure, accumulating the liquid in hot and cold reservoirs disposed beyond opposite ends of the enclosure. The reservoirs `can each be provided with heat transfer coils ,enabling indirect heat exchange in both a refrigerating and aheating sense with respect to the liquid in oscillatory ow. To maintain a sharp cut olf between cold liquid and hot liquid, two immiscible liquids can be employed jointly, one being reserved for hot heat exchange and the other for cold heat exchange, suicient quantities of each being provided so that there is available a large enough It is also possible to obtain a staging effect by fabricating a unitary vehicle, or thermomagnetic operating means, which varies in composition progressively, in zones or in infinitely variable fashion, with respect to its length or some other dimensional aspect in a manner which confers a transition related to temperature under the influence of either a single magnetic field, or a succession of different fields spaced along the vehicle, such that the overall heat transfer range is expanded proportionally.

A vehicle which is thus varied, or which in other words possesses a gradient in composition or properties as covered in the preceding discussion, need not be a single object or article or unitary in nature. The vehicle may exist as a mass Whose limits are generally defined by a suitable containing means or which may exist as a distributed mass supported, or carried by, or in a Huid, solid, or gel-like medium; and having its composition and characteristics maintained in a varied or graded condition with respect to some predetermined dimensional aspect or geometrical co-ordinates.

A gradient object, as referred to herein, is an object comprising a material capable of undergoing a first order solid-phase-to-solid-phase transition as defined herein, said material having a composition varied angularly about a point or axis or varied along one or more selected lines, which need not be straight lines, in the object such as to display said transition at successively higher temperatures in a first path or direction along or about said point or axis or said line, and at successively lower temperatures in an opposite path or direction.

Gradient objects or units are a particularly useful form for materials exhibiting a first order solid-phase-to-solidphase transition. Such objects can be used in energyconverting devices for many purposes, e.g., as temperature indicators, as cores in temperature-sensitive inductors, transformers, and the like, and as an element in thermal switches. In many such uses, the gradient feature permits ready and precise adjustment of device operation to suit particular environmental conditions.

FIGURE XII shows various illustrative examples of units or objects having useful gradients of composition.

The following examples illustrate preparation and application of gradient objects:

EXAMPLE A A manganese-chromium-indium antimonide containing (by weight) 45.40% Mn, 50.02% Sb, 2.10% Cr, and

2.48% In was prepared by melting the powdered elements in the indicated proportions and casting into a copper mold. The solid casting, which has a solid-phaseto-solid-phase transition over a broad temperature range from about C. to about 35 C., was cooled in liquid nitrogen and ground under liquid nitrogen to small particle size. The ground material was separated magnetically at a series of temperatures into 10 fractions. The temperature at which these fractions undergo a solidphase-to-solid-phase transition decreases progressively from one fraction to the next, in such manner that the particles of successive fractions are not attracted by a magnet at 33, 30, 29, 28, 27, 26, 25, 24, 22, and below 22 C., respectively. These fractions were loaded successively into a 4 mm. (ID.) glass tube sealed at one end, making a column about 90 mm. in length. The open end of the glass tube was closed with a tight fitting stopper. rThe gradient object so produced assumed a `position in a magnetic field dependent on the temperature of the object and could be employed as a temperature indicator.

EXAMPLE B Manganese-chromium-indium antimonide was prepared by melting the powdered elements in proportions corresponding to the formula MnLggCrumSbo'gInom in an alumina Crucible under an atmosphere of argon. Aluminum (0.11% by weight based on the total of Mn, Cr,

Sb, and In) was added as a chalcogen reactive reagent,

as described in application Serial No. 120,679, filed lune 29, 1961, in the name of W. W. Gilbert. After solidiication, the products from two such preparations were combined, out-gassed at 400 C. under a pressure of 0.1 micron, and melted under purified argon. Vacuum was applied and the melt was cast into the form of a rod 1/s in diameter by pouring into a copper mold heated to 400 C. at the lower end to promote iiow. A portion of the rod, about 5.5" in length, was used as cathode in a chromium plating cell (FIGURE VI). The anode 101 of the cell is a sheet of lead foil (5 mils in thickness and 15 cm. wide), rolled into the shape of a frustum of a cone having a large diameter of 5.5 cm. and a height of 12 icm. The small diameter, 0.75 cm. of the frusttun was such that it readily accommodated a small glass insulating sleeve 102 slipped over one end of the cathode. The anode and cathode were assembled as indicated in FiGURE VI. The electrolyte 103 was a chromic acid solution containing 250 g. per liter of CrO3 and 2.5 g. per liter of H2SO4. The cell and electrolyte were heated to 5060 C. and a current of 7 amperes at a potential difference of 5 volts was passed through the cell for 20 minutes. Chromium was plated on the manganesechromium-indium antimonide cathode 104 in an amount of 0.112 g. over a length of 3.4 inches. Of this length, the portion adjacent to the small diameter of the conical frustum anode received the heaviest chromium plate, and the plate decreased progressively to the portion of the cathode rod adjacent to the large diameter of the frustum. In other words, a gradient chromium plate was produced.

The manganese-chromium-indium antimonide rod bearing the -gradient chromium plate was removed from the plating bath, rinsed in distilled water, dried and out-gassed by heating to 400 C. under l0.1 micron pressure. The plated rod was then l'annealed to 875 C. for 47 hours in an atmosphere of purified argon to cause the chromium plate to diffuse into the rod, thereby producing a manganese-chromium-indium antimonide rod having a gradient in chromium concentration along the length of the rod. The rod was cooled from the annealing temperature to room temperature at a rate of 30 C. per hour.

The magnetic response as a function of temperature of the gradient rod, prepared as described above, was measured at various locations along the length of the rod. For this measurement, the gradient rod was inserted in a transformer located near the center of a heater tube provided with a thermometer. The transformer, consisted of separate primary and secondary windings fwithin which were inserted soft steel sleeves 1A" LD. by 1% O.D., each having a flange ('s diameter by 1A" thick) at one end. The ends of the sleeves not carrying a flange were adjacent to one another and separated by a distance of 1A. The primary coil was energized with 6.3 volt A.C. current and the out-put of the secondary coil after rectification with a half-wave rectifier lwas measured by a D.C. volt meter (0-300 microvolt range). The out-put at several temperatures as a function of position along the rod is illustrated in FIGURE VII. From the figure it will be observed that as the temperature of the rod increased, more and more of the rod became magnetic. This is illustrated in another way in FIGURE VIII in which the location along the rod at which the so-lid-phase-to-solidphase transition is 501% complete is plotted as abscissa and the temperature as ordinate.

In addition to `objects prepared according to the above examples, self-supporting gradient objects are also prepared from graded powders by loading the powders consecutively into a die suitable for producing the shape desired in the nal object and compressing at a pressure of about 20,000 p.s.i. Additional strength may be acheved by sintering at elevated temperatures. Gradient objects are also prepared by dispersing particles of material having a first order solid-phase-to-solid-phase transition in a matrix, e.g., an organic polymer such as a vinyl 13 polymer composition, polyethylene, polyhexarnethyleneadipate, and polyethylene glycol te'rephthalate.

Gradient objects prepared from material having a solidphase-to-solid-phase transition in particulate form are readily modified, if desired, by incorporation of other materials also in particulate form prior to fabrication. The added materials can be uniformly or non-uniformly distributed throughout the object. Among such other materials, magnetic materials having the usual dependence of magnetization on temperature, for example, iron oxide, chromium dioxide, iron, cobalt, barium ferrite, and the like, are especially useful. It is sometimes desirable to align the particles magnetically with the easy direction of magnetization aligned as desired for optimum results.

Illustrative of compositions useful in gradient objects or as the vehicle in refrigerators of the type described are manganese-chromiurn-indium lantimonides having a tetragonal crystal structure of the CuZSb type (P4/umn). Such compositions have cleavage planes perpendicular to the c-axis and have Curie temperatures usually in the range of 180-300 C. The compositions usually melt at about 900 C. or above and exhibit densities in the range of 7.0-7.2 g./cc. at room temperature. Some compositions exhibit a thermal hysteresis in transition, i.e., the transition occurs at la higher temperature when approached from a temperature below the transition than when approached from a temperature above the transition. When temperature hysteresis is of suicient magnitude to interfere with operation `of a refrigerator or gradient object device, hysteresis can usually be reduced to acceptable levels by 'an increase in applied magnetic field at an appropriate stage in the hysteresis cycle. Other properties of vcertain manganese-chromium-indium antimonides are Ytabulated below.

Table I PROPERTIES OF MANGANESE-'CHROMIUMLINDIUM ANTIMONIDES Property Value (at 300 K.)1

Yungsfnodulus (single crystal sample) 13.3 101l dynes/cm.2

Shear modulus (polycrystalline sample) 3.0Xl011 dynes/cm.2

Hydrostatic pressure coefcient 2 7,500 p.s.i./ C.

Uniaxial anistropy field (easy direction) 3- 7,200 gauss.

Maximum saturation per gram 27 gauss cm/g. 41 gauss cm/g. (100 K).

Magnetic field coeicient 4 2,700 oerstedsfJ C.

Heat capacity at constant pressure 0.095 calories/g." C.

Latent heat of transition 0.4 calorie/g.

Thermal conductivity 0.06 watt/cm. C.

1 Values interpolated for 300 K. from values measured on manganesechromiun-indium antimonide samples havingtransition temperatures nerCiQngIein pressure per degree change in transition temperature at constant field.

3 For a composition having atransiticn temperature of 200 K.

4 Change in field per degree change in transition temperature at constant pressure.

Another embodiment of 'the invention is a multistage refrigerator employing movable vehicles is illustrated in FIGURES IX, X and XI. In the figures the vehicles 41 are disks 0.080" in thickness and 1.25" in diameter. The vehicles are movably mounted between heat source elements and heat sink elements 42 and 46 which are held rigidly in position by mounting rings 43 constructed of 'non-magnetic, thermally insulating material. The source elements, sink elements, 'and vehicles are sealed against air leakage by O-rings 44 of silicone rubber. The mounting rings are bored to provide vacuum inlets 45 and 49 which are in communication with a 'manifold structure partially shown. The vehicle disk can be a casting or a sintered Iobject prepared from a material having a first order solid-phase-to-solid-phase transition or dispersion of such a material in particulate form in a binder. It is desirable that the easy direction of magnetization be perpendicular tothe faces of the disk and that the binder, if

` employed, be held to the minimum amount necessary to provide adequate structunal strength. The vehicle disk for a typical heat pump stage, whose operation is de- 14 scribed below, was prepared by machining to the desired size ya mosaic of closely fitted large crystals of a manganese-chrornium-indium antimonide, having a `first order solid-phase-to-solid-phase transition at 4about 28 C., held together with methacrylate resin.

The heat -source elements and heat sink elements are preferably disks of laminated construction formed by winding alternate ribbons (0.25 in width and ca. 10 mils in thickness) of copper (for high thermal conductivity) and an iron-co `,alt alloy containing about equal parts of iron andcobalt (for high magnetic saturation) into a tight spiral. The spiral is impregnated under a Vacuum with an epoxy resin which, after curing, prevents the spiral from unwinding. A ring of epoxy resin 48 is provided which serves :as a support tor holding the disk in the mounting rings. After curing of the resin, the disk and support are machined to the desired dimensions. In one embodiment of this device, whose operanon is described bellow, the disk was 0.25 in thickness and 1.25 in diameter, and the ring was 0.070 in thickness and 1.50H in diameter. It will be apparent from the drawing figures that any desired number of such stages can be combined/the heat source of one stage serving as the heat sink for the adjacent stage. In such an assembly the terminal stages are usually provided with means (not shown), e.g., fins, heating or cooling coils, and the like, to permit utilization of the heating and/ or cooling effects produced. The Whole assembly is placed in operative association with an electromagnet (shown schematically in FIGURE XI) capable of providing a periodic magnetic field in the direction indicated by rarrows 47.

In operation, motion of Ia vehicle disk is coordinated in time with application of the magnetic fiel-d to provide heat transfer between source and sink by an arrangement shown schematically in FIGURE XI. For example, when the vehicle is held in contact with disk 46 by application of vacuum through orifice 49' Iand a magnetic field is concurrently applied, the vehicle will absorb heat from disk 46. :If the vacuum is then released from orifice 49 and applied to orifice 45 and at the same time the magnetic field is eliminated or substantially reduced, the vehicle wili be pulled into contact with disk 42 and will liberate heat thereto. A model of this device operating With a cycling time of approximately l second produced a temperature difference of about 0.3 C. per stage between source and sink. A suitable control means such as control valve 202 may be utilized to control the pressure applied fto move the vehicle elements.

It will be understood that various types and combinations of xed 'and mobile vehicle with stationary or mobile sources and sinks are within the scope of this invention, including, specifically, those employing fluidized or entrained solids techniques, land that no limitations as to the physical form of the co-operating agencies are to be implied from the foregoing description of preferred embodiments.

It is moreover possible to Vobtain various desired oontrol effects by interposing magnetic shielding cyclically, or as particular fixed patterns, between the magnetic poles and the vehicle, and to yotherwise modify widely the -method and apparatus of .this invention without departure from its essential spirit, and it is therefore intended to be limited only -by the appended claims.

I claim:

l. A method of effecting heat transfer utilizing a substance which idisplays a rs=t-order solid-phasedo-solid* phase transition with accompanying relatively large change in internal energy content under the inuence of a magnetic field comprising exposing said substance to a magnetic field preselected so as to induce said substance to traverse said transition from `a first solid state phase to a second sollid state phase, and thereafter effecting heat transfer with respect to said substance as a consequence of conversion to said second state. i

2. A method of effecting heat transfer according to claim 1 wherein said first-order solid-phase-to-solid-phase transition ris traversed cyclically and repetitively :from one sai-d solid state phase to the other.

3. Apparatus for effecting heat transfer comprising in combination a heat transfer vehicle consisting of a substance which displays a first-order solid-phase-to-solidphase transition with accompanying relatively large change in internal energy content under the influence of a magnetic field, a heat source having a temperature adapted to maintain a discrete tempenature differential with respect to said vehicle when said vehicle exists in a first solid state phase, a heat sink having a temperature adapted to maintain a discrete temperature differential with respect to said vehicle when said vehicle exists in a second solid state phase, means adapted to impress a magnetic field upon said vehicle to traverse said vehicle through said first-order transition, and means co-'ordinated in time with respect to traversal of said transition establishing a heat flow path selectively and sequentially between said heat source land said vehicle and between said heat sink and said vehicle.

4. Apparatus `according to claim 3 wherein said heat transfer Vehicle is composed of material having a composition varied in the direction of the length of said vehicle such as to display said -transition at successively higher temperature in a first direction along said length and at successively lower temperatures in a direction opposite to said first direction along said length.

5. Apparatus for effecting heat transfer comprising in combination :a mobile heat transfer vehicle consisting of a substance which displays a first-order solid-phase-tosolid-phase tnansition with accompanying relatively large change in internal energy content under the influe-nce of a magnetic field, a fixed heat source having a temperature adapted to maintain a `discrete temperature differential with respect to said vehicle when said vehicle exists in -a first solid .state phase, a fixed heat sink having a temperature adapted to maintain a discrete temperature differential with respect to said vehicle when said Vehicle exists in a second solid state phase, means adapted to impress a magnetic field upon said vehicle to traverse said vehicle through said first-order transition, and means co-ordinated in time with respect to traversal of said transition adapted to move said vehicle into heat transfer relationship selectively and sequentially with said fixed heat source and with said fixed heat sink.

6. Apparatus for effecting heat transfer according to claim 5 wherein said heat source Aand said heat sink are disposed vertically apart one from another and wherein said means :adapted to impress said magnetic field upon said vehicle effecting traversal of said vehicle through said first-order transition is employed conjoint-ly to elevate said vehicle from the lowerxnost one of the pair consisting of said source and said sink to the uppermost one of said pair and the force of gravity is employed for return of said vehicle to said lowermost one of said pair.

7. Apparatus for effecting heat transfer comprising in combination a mobile heat transfer vehicle consisting of a slug of a substance which displays a first-order solidphase-to-solid-phase transition with accompanying relatively large change in internal energy content together with a change in state from substantially non-magnetic to magnetic under the influence of a magnetic field, a fixed heat source having a temperature adapted to maintain a discrete temperature differential with respect t0 said vehicle when said vehicle exists in a first solid state phase, a fixed heat sink having a temperature adapted to maintain a discrete temperature differential with respect to said vehicle when said vehicle exists in a second solid state phase, said source and said sink being disposed Vertically apart one from another with said slug disposed therebetween, means retaining said slug substantially within the region bounded at the ends by said source and said sink, means adapted to repetitively impress a magnetic field upon said slug to traverse said slug in one direction through said first-order transition and conjointly elevate said slug when in said magnetic one of said states from the lowermost one of the pair consisting of said source and said sink to the uppermost one of said pair during increase of said magnetic field and to traverse said slug in the opposite direction through said first-order transition with gravity return of said slug to said lowermost one of said pair during decrease of said magnetic field.

8. Apparatus for effecting heat transfer according to claim 7 consisting of a multiplicity of stages arranged with heat sources and heat sinks 4in alternation, and wherein the slug within each individual stage is preselected with respect to chemical composition so as to preserve progressive heat transfer throughout successive stages of the apparatus.

9. Apparatus for effecting heat transfer comprising in combination a xed heat transfer vehicle consisting of a substance which displays a first-order solid-phase-to-solidphase transition with accompanying relatively large change in internal energy content under the influence of a magnetic field, a first body of fluid constituting a heat source having a temperature adapted to maintain a discrete temperature differential with respect to said vehicle when said vehicle exists in a first solid state phase, a second body of fluid constituting a heat sink having a temperature adapted to maintain a discrete temperature differential with respect to said vehicle when said vehicle exists in a second solid state phase, means adapted to impress a magnetic field upon said vehicle to traverse said vehicle through said first-order transition, and means co-ordinated in time with respect to traversal of said transition establishing a heat flow path selectively and sequentially between said heat source and said vehicle and between said heat sink and said vehicle.

l0. Apparatus for effecting heat transfer according to claim 9 wherein said first body of iiuid and said second body of fluid are liquids immiscihle with one another.

1l. Apparatus for effecting heat transfer comprising in combination a fixed heat transfer vehicle consisting of a substance which displays a first-order solid-phase-to-solidphase transition with accompanying relatively large change in internal energy content under the influence of a magnetic field, a first heat reservoir connected in closed iiuid flow circuit with respect to said heat transfer vehicle through first valve means, said first heat reservoir containing a body of liquid constituting a heat source having a temperature adapted to maintain a discrete temperature differential with respect to said vehicle when said vehicle exists in a first solid state phase, a second heat reservoir connected in closed fluid flow circuit with respect to said heat transfer vehicle through second valve means, said second heat reservoir containing a body of liquid constituting a heat sink having a temperature adapted to maintain a ydiscrete temperature differential with respect to said vehicle when said vehicle exists in a second solid state phase, means adapted to impress a magnetic field upon said vehicle to traverse said vehicle through said first-order transition, means adapted to impel liquid from said first heat reservoir exclusively through said first valve means and past lsaid heat transfer vehicle during at least a portion of `the time in which said vehicle exists in said first solid state phase, means adapted to impel liquid from said second heat reservoir exclusively through said second valve means and plast said heat transfer vehicle during at least a portion of the time tin which said Vehicle exists in said second sol-id state phase, and means co-ordinated in time with respect to traversal of said transition operating said first and second valve means in la sequence such as to effect contacting of said Vehicle with liquid from said first and said second heat reser-voirs in appropriate relationship with respect to operation of said means adapted to impress said magnetic field upon said vehicle to traverse said vehicle through 1 7 said rst-order transition so as to effect heat transfer through said vehicle from said iirst heat reservoir to said second heat reservoir.

12. Apparatus for effecting heat transfer comprising an open uid flow circuit consisting of a first heat reservoir connected through a fixed heat transfer vehicle with a second heat reservoir, said heat transfer vehicle consisting of a substance which displays a first-order solid-phaseto-solid-phase transition with accompanying relatively large change in internal energy content under the influence of a magnetic field, a body of liquid contained fwithin said -iiuid iiow circuit constituting with said tirst heat reservoir a heat source having a temperature differential with respect to said vehicle when said vehicle exists in a first solid state phase and with said second heat reservoir a heat sink having a temperature differential with respect to said vehicle when said vehicle exists in a second solid state phase, reversible pumping means connected in series With said fluid ow circuit, means adapted to impress a magnetic eld upon said vehicle to traverse said vehicle through said irst-order transition, and means co-ordinated in time with respect to traversal of said transition causing said reversible pumping means to impel said liquid in alternation in preselected directions past said heat transfer vehicle to effect heat transfer through said vehicle from said first heat reservoir to said -second heat reservoir.

13. As an article of manufacture, a thermomagnetic substance which displays a iirst order solid-phase-to-solidphase transition with accompanying relatively large change in internal energy content under the influence of a magnetic field, said substance forming a coherent threedimensional shaped mass, said mass having a plurality of portions, each of said portions having a composition varied with respect to the compositions of the other portions so that the temperature zone at which said transition occurs in each said portion is varied with respect to that of the other portions, said portions being positioned and arranged in said mass with respect to one of said dimensions of said mass in sequential order of composition differential and increasing transition temperature level.

14. As an article of manufacture, a body of thermomagnetic material comprising a substance possessing a iilst order solid-phase-to-solid-.phase transition with accompanying relatively large change in internal energy content together with a change in state from lower to higher intrinsic magnetization under the influence of a magnetic lield, said body having an elongated coherent form and comprising a plurality of zones, the material in each zone comprising a substance having a composition varied with respect to the compositions of the substances in the other zones so that the temperature level at which the transition occurs in each zone is Varied with respect to that of the other zones, said zones being positioned and arranged within said body in a sequential .order of increasing transition temperature levels.

15. The article of claim 14 in which said Zones are positioned and arranged in said order relative to the longitudinal dimension of said body.

16. A thermomagnetic component for use in a thermomagnetic device, said component comprising a rigid shaped three dimensional body of material exhibiting a rst order solid-phase-to-solid-phase transition with accompanying relatively large change in internal energy content under the influence of a magnetic iield, the temperature level at which said transition occurs being to a limited degree variable in response to variation in pressure exerted on said material, said body comprising a plurality of portions, each of said portions comprising material having a composition different with respect to the compositions of the other portions so that the temperature level at which the transition occurs in each portion differs from that at which the transition occurs in said other portions, said portions positioned and arranged Within said body in a sequential order of graduated composition transition temperature levels, said component in combination with a means operatively cooperating with at least one of said portions for varying the pressure thereon.

17. The component of claim 16 in which said portions are positioned and arranged in said order relative to single dimensional respect of said body.

18. For use in a thermomagnetic device, a thermomagnetic component comprising a body of material which comprises a substance possessing a first order solid-phaseto-solid-phase transition with accompanying relatively large change in internal energy content under the inuence of a magnetic eld, the temperature zone at which said transition occurs being to a limited extent variable in accordance with the intensity of an applied magnetic iield and with the magnitude of external pressure to which the material is subjected, said component in combination with operatively associated means for selectively varying at least one of the conditions of field intensity and external pressure, said body of material having a coherent three dimensional form with a plurality of portions, each of said portions comprising a quantity of said substance having a composition varied with respect to the compositions of the other portions so that the temperature zone in which the said transition occurs in each said portion is significantly varied with respect to that of the other portions, said portions positioned and arranged in said body of material in predetermined sequence of ascending transition temperature zones.

19. A thermomagnetic control means for a thermomagnetic device, said control means comprising a supporting means and a plurality of elements supported in the supporting means, each of said elements comprising a substance exhibiting a first order solid-phase-to-solidphase transition with accompanying relatively large change in internal energy content under the influence of a magnetic iield, the substance of each of said elements varying with respect to the substance of said other elements as to the temperature level at which the transition occurs, said elements generally positioned and arranged Within said supporting means in a sequential order of graduated transition temperature levels of the substance involved.

20. The thermomagnetic control means of claim 19 which further comprises a means operatively associated with said supporting means and at least one of said elements for subjecting at least one of said elements to a variation in pressure in order to vary in a predetermined manner the transition temperature level of the substance of Which said element is comprised.

21. For use in a thermomagnetic apparatus, a thermomagnetic operating means capable of producing relatively large unidirectional changes in its transferable internal energy at a plurality of given temperature levels in response to the application of a unidirectionally changing magnetic field thereto, in combination and in operative association with an adjustable means for selectively varying said temperature levels as desired within limits.

References Cited in the tile of this patent UNITED STATES PATENTS 2,589,775 `Chilowsky Mar. 18, 1952 2,780,069 Olcott Feb. 5, 1957 2,970,961 Mathias Feb. 7, 1961 2,989,480 Mathias .Tune 20, 1961 2,999,777 Yarmartino Sept. l2, 1961 2,999,778 Mendelsohn Sept. 12, 1961 

1. A METHOD OF EFFECTING HEAT TRANSFER UTILIZING A SUBSTANCE WHICH DISPLAYS A FIRST-ORDER SOLID-PHASE-TO-SOLIDPHASE TRANSITION WITH ACCOMPANYING RELATIVELY LARGE CHANGE IN INTERNAL ENERGY CONTENT UNDER THE INFLUENCE OF A MAGENTIC FIELD COMPRISING EXPOSING SAID SUBSTANCE TO A MAGNETIC FIELD PRESELECTED SO AS TO INDUCE SAID SUBSTANCE TO TRAVERSE SAID TRANSITION FROM A FIRST SOLID STATE PHASE TO A SECOND SOLID STATE PHASE, AND THEREAFTER EFFECTING HEAT TRANSFER WITH RESPECT TO SAID SUBSTANCE AS A XONSQUENCE OF CONVERSION TO SAID SECOND STATE. 